Improvement in expanding screw-taps



UNITED STATES.

PATENT'QFHCE- JOHN BROWN DOUGLAS, OF PHILADELPHIA, PENNsYLvANiA, AsslcNoR To MORRIS, TAsKERAa OO., (mnrrnng or SAME PLAGE.

IMPROVEMENT IN EXPANDING SCREW-TAPS.

Specification forming part of Letters Patent No. 189,889, dated April Q4, i877; application Vfiled .i March 3, 1877.

To all whom it may concern Be it known that I, JOHN BROWN DOUGLAS, of the city and county of Philadelphia, in the State of Pennsylvania, have invented a new and useful Expanding Screw-Tap, of which I do hereby declare the following lspecification to be a full, clear, and precise description, and sufficient to enable those skilled in the art to which my invention appertains to comprehend and construct it, reference being had to the accompanying drawings, which form part of this specilication, and represent a tap embodying my invention- AFigure' 1 being a central vertical section thereof; Fig. 2, a side elevation; Fig. 3, a cross-section on the line a b of Fig. l; and Figs. 4 and 5, cross-sections on the line c d of Fig. 2, respectively, showing the` tap-cutters expanded and retracted.

Similar letters of reference indicate corresponding parts in all the iigures.

This invention belongs to the class of ltaps for cutting interior threads, which are termed expanding 7 taps, and are so constructed that after the tap is entered, and the screwthread cut, the thread-cutting jaws can be retracted inward out of the threads, so that the tool eanbe withdrawn at once without screwing it out.

My improvement is constructed as follows:

, A is the stock, square-headed at a, to facilitate attachment to a lathe or other spinning device, and Haring out to form a head, B. G is the eccentric stem of a stock, being, in effect, a cam-shaft formed with four longitudinal crests, c c c c, and four longitudinal hollows, c c c c', as clearly shown in the sectional views 4 and 5.

D is the shell, a slightly-tapered hollow cylinder surrounding the eccentric stem, abutting at top against the stock-head B, and retained in place by the cap E, which is itself secured by a screw, E', taking into the extremity of the eccentric stem. y

The shell is provided with four longitudinal slots, in each of which is snugly but movably fitted a thread-cutting jaw, F. l

ff are springs, fitted transversely through the inner portion of said jaws, and acting against the inside walls of the shell in suchy manner that, ordinarily, the cutting-surfaces ,of the jaws are held in, so as to project but slightly from the exterior of the shell; the tension is, however, such that sufficient force upon the backs of thev jaws will compress the springs, and cause the jaws to project.` The jaws are slightly tapered or inclined.

G G are reamer-cutters, rigidly iixed in the shell, and set to ream in a direction the reverse of the cutting of the tapcutters. They project more than the jaws when the latter are retracted, and less than the same when expanded. They also are suitably tapered.

H H are lugs on the upper portion of the eccentric, which play in quadrant-shaped recesses I I in the top of the shell, as very clearly shown in Fig. 3, andserve to limit the throw of the shell, whereof hereafter. J is a `handle to assist in throwing or rotating the shell. In use it fits into the socket J in the shell.

Such being the detail of mechanical construction of my invention, by consulting Figs. 4 and 5 of the drawvng it will be readily seen that the tap-cutting jaws are operated by theV eccentric stem upon rotation of the shell to the extent of its throw in a right or left hand direction about said stem; that in the position represented in Fig. 4 the tap-cuttersv are expanded or forced out from the shell by the crests of the eccentric, over which the rotation forces them, the springs being compressed; while in that shown in Fig. 5 the cutters, resting in the hollows of the eccentric, are held in, or retracted by, the expanding action of their Springs.

The studs limit the throw of the shell, and are adjusted so that in one position they bring the jaws upon the summits of the crests, and in the other over and (thence by the springs) into the hollows. They further hold the shell in fixed conjunction with the stock, enabling the reamers to work when one position has been assumed, and the thread-cutting jaws when the other.

Any number ofjaws may, ofcourse, be employed, the slots in the shell and crests and hollows on the eccentric being made correrespondent, and any it system of springs other than that represented.

Having thus described my invention, what I claiml,and desire to secure by Letters Patent of the United States, is

1. In a screw-threaded tap, thread-cutting jaws F, adapted to be both radially projected by an eccentric, C, and radially retracted by springs f.

2. In a screw -cutting tap, thread-cutting jaws F, set radially through the shell D, in combination with springsf, and with au eccentric, G, provided with crests c and hollows c', as and for the purposes set forth.

3. In combination with the shell D, lugs H on the stock A to limit the throw ot' the shell, substantially as and for the purposes set forth.

4. In combination with the shell D reamercutters G, set so as' to project beyond the thread-cutting jaws F when the latter are re# tracted, (and in such relation adapted to ream in a direction the reverse of the cutting of the jaws,) and to be within the cutting-line of said jaws when the latter are projected, substantially as specified.

5. A screw-cutting tap, provided with both xed reamer-cutters and thread-cutting jaws, and thereby adapted to be used as both a tap and a reamer, substantially as shown and 'described.

6. The combination of the jaws F and their springs f with the stem C, having' hollows c', the springs adapted to retract the jaws into the hollows, and the hollows to receive the jaws, substantially as described.

In testimony whereof I have hereunto signed my name in the presence of two subscribing witnesses.

JNO. B. DOUGLAS. Witnesses: p

J. 'BoNsALL TAYLOR, J oHN J OLLEY, Jr. 

